According to the President's New Freedom Commission report, the ability to improve our understanding of childhood psychopathology has great public health significance. Mental health conditions cause one in ten children to suffer significant impairment at home, at school, and in the community. Critical to the Healthy People 2010 objective of reducing the prevalence of mental disorders among young people is a clearer understanding of the developmental processes underlying childhood psychopathology. In children, adolescents, and adults, comorbidity is the rule, rather than the exception. Yet to date most research on child and adolescent psychopathology has either disregarded the presence of or eliminated participants with co- morbid disorders. Neither approach is useful towards the end of addressing the needs of the majority of persons with mental health conditions who have co-occurring problems. The purpose of the proposed research is to explicate the development and resolution of co-occurring and non-co-occurring depressive and conduct problems by studying adolescents as they move into a period of marked escalation and gender differentiation in risk for major depressive, conduct, and substance abuse disorders. The proposed research project addresses key questions that have emerged regarding comorbidity by taking advantage of a unique opportunity to assess late adolescent psychopathology and related constructs in a community-based sample that has an overrepresentation of adolescents at risk for comorbid and non- comorbid depressive and conduct problems. The sample includes both girls and boys, is racially diverse, and was well-characterized, using a repeated measurement design with six assessments during the early adolescent years (6th-9th grades). In the proposed study 450 adolescents and a parent/guardian will undergo in- person interviews in the 12th grade. The research addresses the question of whether comorbidity is a developmental phenomenon of early adolescence. To this end both dimensional and categorical approaches will be used to determine the extent to which forms of psychopathology change from non-specific (mixed symptom presentation) to specific (presentation consistent with a specific form of adult psychopathology) over the course of adolescent development. Risk factors that contribute to escalating pathways towards specific and comorbid disorders and protective factors that mitigate early vulnerabilities to psychopathology will be identified. Functional outcomes in the areas of school, vocational, and social relationships of adolescents with comorbid and non-comorbid depressive and conduct problems will be compared to adolescents with neither form of psychopathology. Gender differentiation in developmental pathways will be explicated. The proposed research addresses a premier challenge facing mental health professionals by providing information that will highlight opportunities for intervention to reduce suffering and adverse consequences from comorbid psychiatric conditions that manifest during the adolescent developmental period.